This invention relates to solar cell modules and more particularly to improved structures in such modules.
The use of solar cells, typically made from single crystal or polycrystalline silicon material, to produce electricity directly from solar insolation is well known. A typical solar cell can provide from one-half to four amperes of current at about one-half volt at peak insolation conditions. The typical commercial unit in which such cells are sold is a module containing one or more series circuits each comprising a plurality of cells sufficient to provide a useful output voltage. For example, thirty to thirty-five cells may be connected in series to provide an output working voltage around fifteen volts.
The delicate solar cell strings are usually laminated to a transparent superstrate using one or more layers of pottant material such as PVB (polyvinyl butyral), EVA (ethylene vinyl acetate) or EMA (ethylene methyl acrylate). A moisture and puncture resistant layer of a plastic and/or metal foil material is often added to the back of such modules for further protection. U.S. Pat. No. 4,067,764 issued to Walker et al. on Jan. 10, 1978 describes a typical solar cell panel and method of assembly using PVB as a pottant and a polyethylene terephthalate film as an outer protective shield. U.S. Pat. No. 4,224,081 issued to Kawamura et al. on Sept. 23, 1980 describes another solar module assembly using a rigid glass substrate.
The most common commercial module described above uses a flexible outer protective shield and depends almost entirely on the transparent superstrate, typically tempered glass, for its structural strength. Such modules are, therefore, difficult to handle and mount. As a result, the commercial modules usually include additional metal frame members, typically extruded aluminum channels, attached to and supporting all edges. The frame members typically interlock and include a groove, often filled with sealent, for tightly gripping the edges of the basic module. Frame members also include various flanges both for structural strength and for providing surfaces which may be used for attachment to supporting structures for a solar array.
It can be seen that in assembly of the basic module described above, there are no structural elements present to prevent sliding of the various laminate layers relative to each other and resulting misalignment. Such sliding may occur when pressure and heat are applied to the structure to cause the pottant layers to fuse together. In addition, the structural frame members are relatively expensive and require considerable hand labor for assembly to the basic module, thereby increasing the cost of the finished product. The reduction in cost of finished solar modules is essential if this renewable energy source is to displace fossil fuel energy sources.